Same issue with Samsung UE50HU6900 (2014) and SEK-3500u (2015). Both have HDMI 2.0 ports and UHD color mode is Enabled. My GPU is Asus Strix R9 285.

With latest Crimson Drivers and clean W10 install I’ve managed to get 2160p@60Hz YCbCr 4:4:4 (8 bit) ONCE. It returned to 30Hz next reboot. DisplayPort handshake failure, or something.

Troubleshooted this issue before with the great Club3D support for about 3 weeks. Firmware was updated and every possible combination was tried by me – including custom EDID-overrides! After a complete rebuild/upgrade my PC to Skylake i7 the issue still remains the same. It’s not a Windows 10 or HDMI cable issue, honestly, with Microsoft basic display driver 2160p@60Hz 4:4:4 works right away.

This adapter does have issues. Do not spend too much time with troubleshooting like I did.